In microwave transmission lines, it is frequently desirable and often necessary to change from waveguide to coaxial line. The problem is to provide for a transition between the principal coaxial TEM-mode and the dominant TE.sub.01 -mode in the rectangular guide.
The fundamental way of establishing a desired mode in a waveguide is the excitation of either the electric or the magnetic field identified with that mode. This usually is done either by means of an antenna element parallel to the electric field or by means of a loop, the plane of which is normal to the magnetic field.
As disclosed in co-pending application Ser. No. 585,142, a plurality of conducting rods may be used to interconnect the clad surfaces of a metal-clad dielectric and to thereby define the side and backwalls of a dielectric filled waveguide. Similarly, the metallic surfaces of the metal-clad dielectric may be oriented such that they define the front and rearwalls of the dielectric filled waveguide and the conducting rods may be placed so that they define the top, bottom and sidewalls of the waveguide. With this latter type of construction, however, the distance between the dielectric filled waveguide front and backwalls is so small that it precludes coupling into the waveguide by normal methods.